This invention relates to conveyor means for placing concrete and more particularly to a hopper construction from which concrete is discharged onto the belt of the conveyor for carrying concrete to the point of deposition.
Concrete varies in consistency depending upon the relative proportions of water-cement and aggregate solids which, in turn, affect the flow characteristics of the mix. The flow is also affected by the size range of the aggregate which occupies 60 to 80 percent of concrete volume. The consistency or workability of the mix may vary from that of a free flowing slurry to a composition which is fairly stiff and resistant to flow. In conveying concrete it is essential that the aggregate be distributed uniformly throughout the mass and that the coarse aggregate does not separate from the sand-cement mortar. For maximum cured strength the cement binder must cure in contact with all of the aggregate.
It is the primary object of this invention to provide a large capacity hopper, say in the range of 8 to 10 cubic yards volume, which is capable of discharging concrete of widely varying consistency in a smooth continuous ribbon onto the surface of a moving belt which accurately places the concrete.
A further object is to provide a discharge hopper of this kind which is capable of handling concrete containing very coarse aggregate including stones up to 4 to 6 inch mean diameter. Another object is to provide a hopper of this kind which discharges the concrete at a rate of 7 to 10 cubic yards per minute without overloading the belt, or causing the concrete to strike the belt with such force that it bounces off the belt and falls to the ground, or is separated from the cement mortar.
It has been proposed heretofore to provide a conical-shaped hopper having a horizontal discharge opening in the bottom which is closed by a sliding door that moves across the opening. This construction permits regulating the volume of concrete which is discharged from the hopper but it is not capable of accurately controlling the direction of the concrete flow. When the sliding door is fully opened the concrete is discharged directly downwardly with great speed and force so that it strikes the moving belt, bounces off the belt and separates the aggregate. If the door is closed to the point where the concrete flows onto the belt at a controlled uniform rate in a continuous ribbon without any undesirable splashing or separation, the capacity of the conveyor is drastically reduced. Furthermore, when the concrete contains large-sized aggregate, such as six-inch stones, they will not pass through the partially-closed opening but instead become lodged between the side wall of the opening and the edge of the door. This further restricts the flow and may even block the opening.
It has also been proposed to provide a clam shell closure pivotally mounted for closing and opening a horizontally disposed opening at the bottom of the hopper. In such a structure when the hinged shells are opened the concrete flows directly down to the belt as described previously in connection with the single closure door construction. The head of concrete in a hopper of the kind herein disclosed may exceed 15 feet. The concrete weighs 135 to 160 lbs. per cubic foot. The force of gravity acting on this extremely heavy mass causes the concrete, and particularly the aggregate therein, to strike the conveyor belt with great force. Unless the flow is carefully controlled the conveyor belt and its supporting structure can be severely damaged by the concrete. Also the aggregate separates from the mortar portion of the mix.
To reduce the force with which the concrete strikes the belt it has been proposed to close the horizontal opening in the bottom of the hopper with a single clam shell which pivots downwardly, about a horizontal axis, away from the opening and serves as sort of a slide for the concrete when in open position. This structure protected the belt from the force of the concrete but was not satisfactory because of its tendency to trap aggregate while closing, thus remaining partially open.
The disadvantages of these prior art structures are overcome and the objectives of the invention are accomplished by providing a hopper having inclined side walls forming the bottom thereof and providing a discharge opening through one of said side walls, which is flat. The side wall opposite the opening serves as a chute or slide and places the moving concrete passing through the opening onto the moving belt in the direction of movement in a continuous ribbon.